The “INESA Lighting Handbook” published by the Illuminating Engineering Society of North America, is incorporated by reference here in its entirety. As discussed in chapter seven of that handbook, a “luminaire” is a device for producing, controlling, and distributing light. It is typically a complete lighting unit consisting of one or more lamps, sockets for positioning and protecting the lamps and for connecting the lamps to a supply of electric power, optical devices for distributing the light, and mechanical components for supporting or attaching the luminaire. Luminaires are also sometimes referred to as “light fixtures.”
Luminaires are usually classified by their application, such as residential, commercial, or industrial. However, a particular luminaire can often be used in more than one application, depending upon its performance characteristics. For example, recessed downlights are used in both commercial and residential applications where they are typically mounted behind a ceiling wall with an opening to produce illuminance on the floor or workplace below.
Various support systems have been employed to carry recessed luminaires in buildings and other structures. For example, recessed fixtures are often suspended between joists, or other parallel support structures, on a pair of “hanger bars” or “bar hangers” extending between the joists. Similar hanger bar arrangements are used to suspend recessed downlights between the rails in a suspended, tile ceiling.
These conventional hanger bars are often formed in one-piece with a fixed length so as to provide adequate structural rigidity at a relatively low cost. For example, U.S. Pat. No. 5,505,419 to Gabrius (assigned at issuance to Juno Lighting) is incorporated by reference here in its entirety and discloses a one-piece bar hanger having a stiffening rib that extends along substantially the entire length of the bar hanger. In order to change its length, the bar must be broken along a single score line. Since the length of the hanger bar cannot be variably adjusted, its use is often limited to joists, or other supports, having a standard and consistent spacing.
Hanger bars have also been devised with an adjustable two-piece configuration. For example, U.S. Pat. No. 5,029,794 to Wolfe (assigned at issuance to Prescolite) is incorporated by reference here and discloses a pair of bar hanger elements that are nested in a slidable relationship relative to each other. Each bar hanger element is identical in construction with an elongated slot and two retaining projections.
U.S. Pat. No. 4,723,747 to Karp et al. (assigned at issuance to Capri Lighting) is also incorporated by reference here and discloses a two-piece bar hanger with an elongated slot as well as a longitudinally extended “dome,” or projection, to facilitate nesting. One of the hanger bar elements has an arrow-shaped retaining projection while the other hanger bar element has a foot-like retaining projection that is received within the slot.
As with single-piece hanger bars, two-piece hanger bars may be trimmed for use with smaller joist spacings. However, these hanger bar assemblies must generally be disassembled prior to altering their length. Furthermore, while such two-piece arrangements permit installation between supports or joists of various spacings, they generally suffer from a lack of stability that fails to provide adequate support for the suspended luminaire, especially when the hanger is installed in its fully-extended, or nearly fully-extended, position.
In this regard, U.S. Pat. No. 6,076,788 to Akiyama (assigned at issuance to Cooper Industries) is incorporated by reference here and discloses a hanger bar assembly with a first bar hanger having a plurality of longitudinal slots, each separated by a reinforcing formation. A second hanger bar member having a plurality of spaced retaining projections is interfitted with the first hanger bar member. At least one of the retaining projections engages at least one of the slots in order to couple the hanger bar members as they are extended longitudinally.
Each of the Akiyama hanger bar members may also include a score line for allowing a portion of the hanger bar member to be removed in order to reduce the overall length of the hanger bar assembly. Although such hanger bar assemblies generally provide adequate support in their fully-extended position, the hanger bar members must be separated in order to change their length by breaking each member along its score line. Furthermore, such conventional hanger bars can generally be used with only one particular type of ceiling configuration.